I deleted the remark about von Neumann while you were composing your reply, after a quick Google search revealed no support for it. (I seem to remember a quote by von Neumann himself where he lamented that his lack of focus had prevented him from being much more productive as a scientist, but this is a very vague memory and I'm now unwilling to rest any claims on it.) For what is worth, here are some relevant remarks on von Neumann's work habits by Herman Goldstine, which contradict my earlier (and now retracted) statement:

His work habits were very methodical. He would get up in the morning, and go to the Nassau Club to have breakfast. And then from the Nassau Club he'd come to the Institute around nine, nine-thirty, work until lunch, have lunch, and then work until, say, five, and then go on home. Many evenings he would entertain. Usually a few of us, maybe my wife and me. We would just sit around, and he might not even sit in the same room. He had a little study that opened off of the living room, and he would just sit in there sometimes. He would listen, and if something interested him, he would interrupt. Otherwise he would work away. [...] So those were his work habits. He was a very methodical worker. Everytime he thought about something, he wrote it down in great detail. There was nothing rough or unpolished. Everything got written down either in the form of a letter or a memorandum.